I don't think it is. AFIAK that's all of the normalisation code right there. IIRC, the front page inherits from MultiReddit internally.
But if your front page is 25 links long (the default) and has 25 subreddits, I imagine adding 2 more means that you need to show 27 subreddits in 25 links, so you hit some edge-case there where things need to be laid out again.
The way this probably works is that we pick 25 subreddits at random (and cache that random choice for a while), some of which may have no qualifying submissions. So you may end up with 2 /r/funny posts, even though you had 27 subreddits for 25 links.
Or at least that's how it used to work. I know this bit has changed but I don't know what the new way is
But if your front page is 25 links long (the default) and has 25 subreddits, I imagine adding 2 more means that you need to show 27 subreddits in 25 links, so you hit some edge-case there where things need to be laid out again.
The way this probably works is that we pick 25 subreddits at random (and cache that random choice for a while), some of which may have no qualifying submissions. So you may end up with 2 /r/funny posts, even though you had 27 subreddits for 25 links.
Or at least that's how it used to work. I know this bit has changed but I don't know what the new way is